It's a dipshit way of teaching you verbs. Here's a cheat sheet: all regular verbs in Italian end in –are, –ere, or –ire. They tend to follow a pretty standard pattern with some deviations but that's beyond this comment so we go beginner mode. Also I am using present tense, again, beginner mode.

Mangiare is an -*Are *verb, so the conjugation is thus:

io (I) mangio
tu (you) mangi
lui /lei (he/she/it) mangia
noi (we plural) mangiamo
voi (you plural) mangiate
loro (it / they plural, also third person respectful) mangiano

see how the -are part of mangiare changes with each subject? Not so much for Tu, but mangii is a stupid-looking word so we don't use it :P

Also I s2g it deliberately dips you on spelling when it shouldn't just to fuck up a perfect score. I've seen it fuck me on a fat fingered mishap one instance, then the next say "I'll allow it but you made a typo" once I've lost the precious